Soil phosphorus fractionations under different fertilization practices on soybean ( Glycine max )-based cropping systems in a Vertisol

Integration of organic and inorganic fertilizers is inevitable to sustain intensive agricultural production; however, assessment of combination of organic and inorganic fertilizers on soil phosphorus (P) fractions is yet to be understood. This study aims to investigate availability, distribution, and fractions of soil P as influenced by long-term fertilization under soybean-based cropping systems in Vertisol. Soil samples were collected during 2021 from a 17-year-old field experiment with six treatments viz., T1: 100% Organic, T2: 75% Organic + 25% Innovative approach, T3: 50% Organic + 50% Inorganic, T4: 75% Organic + 25% Inorganic, T5: 100% Inorganic, and T6: State recommendation under soybean-wheat, soybean-mustard, and soybean-chickpea cropping systems at two soil depths after wheat, mustard, and chickpea, and examined for 0.5 M NaHCO3-P, total P, inorganic P, and different P fractions namely, saloid-P (1 M NH4Cl), aluminium-P (0.5 M NH4F), iron-P (0.1 M NaOH), calcium-P (0.25 M H2SO4), and reductant soluble-P (0.3 M Na3C3H6O7 + 1 M NaHCO3 + Na2S2O3). Results demonstrates that continuous fertilization using organic, inorganic, and their combination influences soil P dynamics. Soybean-chickpea system was found better in sustaining P availability. Higher NaHCO3-P was observed under 50% organic + 50% inorganic plot. Inorganic fertilizer dominated soil P accumulation as observed from higher inorganic fractions, and total P. Addition of organic manure could contribute to solubilization of fixed-P fractions and renders plant available form. It can be concluded that fertilization with organic manures and inorganic fertilizer should be followed so that 25–50% costly P-fertilizers could be saved for crop production under soybean-based cropping systems in Vertisols.